Color printing

ABSTRACT

Porous intermediates printed with color transfer images serve as barriers during heat transfer of dye simultaneously from imaged intermediate and overlying dye transfer source sheet to provide brilliantly colored image and background areas on receptor sheet or film.

United States Patent D bvi Mar. 14 1972 [54] COLOR PRINTING 2,770,53411/1956 Marx, .lr. ..41/41 3,121,650 2/1964 Meissner .1..156/240 [72]Invent Paul 3,280,735 10/1966 Clark et al. .101/149.2 [73] Assignee:Minnesota Mining and Manufacturing 3,330,711 7/1967 Marx, Jr. et al.....1 17/38 Company, St. Paul, Minn. 3,360,367 12/1967 Stricklin....1l7/1.7 X 3,379,526 4/1968 Limberger et al. ..96/1 [221 19693,453,310 7/1969 Arneth et a1 ..96/1.2 [21] Appl. No.: 869,008 3,490,3711/1970 Games ..117/1.7 X

Primary ExaminerRobert F. Burnett [52] US. "117/38, l AssistantExaminer-Raymond Linker, Jr.

1 36.7, 1 17/ 37 R Attorneyl(inney, Alexander, Sell, Steldt & Delahunt[51] Int. Cl ..B4lm 5/00 [58] Field of Search ..1 17/1 .7, 36.2, 36.7,38,138.8, [57] ABSTRACT 30 u 8/2 5 Porous intermediates printed withcolor transfer images serve as barriers during heat transfer of dyesimultaneously from [56] References Cited imaged intermediate andoverlying dye transfer source sheet to provide brilliantly colored imageand background areas on UNITED STATES PATENTS receptor Sheet or Sanders..117/1.7

6 Claims, 2 Drawing Figures PATENTEDMAR 14 m2 3,649 33 2 I N VENTOR0006M: #076 we COLOR PRINTING This invention relates to the preparationof colored prints, and has for a major object the preparation ontransparent film of colored prints wherein the image areas may be in oneor several colors and the background areas in another color, the printsbeing useful as color projection transparencies.

A method of making prints of multicolored originals in full color hasrecently been described in Wiese application Ser. No. 728,167, andapparatus useful in accomplishing such method has been described inDybvig et al. application Ser. No. 728,169 now abandoned, both filed onMay 10, 1968. The method involves exposing a series of photosensitivedye transfer sheet segments to a light pattern from the multicolororiginal through appropriate monocolor filters, developing a transposeddifferentially radiation-absorptive pattern at each segment, and brieflysubjecting each patterned segment to intense radiation while in registryand in contact with a receptor sheet to transfer the appropriatecomplementary dyes from the segment to the receptor.

The apparatus includes a vacuum platen means for supporting the dyetransfer sheet against and in close pressure contact with the receptorsheet. The receptor must therefore be porous; and porous paper, or filmwhich has been perforated to provide porosity, is therefore commonlyused as the receptor sheet. But papers of sufficient porosity to permitclose contact with the transfer sheet are found to permit passage ofvolatile dyes. As an example, such paper is found to be inadequate as aliner when wound up in a roll of the segmented source sheet. Undermoderately prolonged storage the volatilizable dyes are found topenetrate through the liner in amount sufficient to cause discolorationof the photosensitive surface coating on the reverse side of the sheet.

In view of the slow migration of dye through the porous paper undernormal storage conditions, it might be expected that the application ofmuch higher temperatures would greatly increase the migration of thedye. Surprisingly, it has been discovered that, under the conditionshere employed, the porous receptor serves as a completely effectivebarrier to the passage of the volatilized dye. Accordingly it has beenfound possible first to form a full-color dye image on a porous receptorby the techniques and with the apparatus to which reference hashereinbefore been made, and then to retransfer the image to a permanentreceptor while simultaneously transferring thereto a different colorexclusively at background or nonimage areas from a color source sheetoverlying the entire area.

In the drawing,

FIG. 1 is an exploded view in perspective showing the relationship ofthe various components in preparing a color projection transparency, and

FIG. 2 is a plan view of the resulting transparency.

Referring to FIG. 1, a permanent receptor 10, which may for example be afull lOXlO inch sheet of clear transparent dye-receptive polyester film,is supported on a suitable platen 11. Segments 12, 13, 14 of temporaryreceptor sheet material which have previously been imprinted withtransfer dye images are placed face down at desired positions on thereceptor 10, as indicated by dotted lines. A further full size portion15 ofa dye source sheet is placed face down over the segments and thereceptor. A heated platen 16 is then pressed temporarily against thecomposite, causing volatilization and transfer of dyes and acorresponding coloration of the receptor 10. The platens are thenseparated and the sheet 10 removed.

The finished product is shown in FIG. 2 as the transparent film 10 nowuniformly colored over the entire background area 17, printed withmulticolored images or designs 18-20, and uncolored at closelysurrounding areas 21-23 corresponding in external dimension to segments12-14 respectively.

EXAMPLE As described in said application Ser. No. 728,167, thephotosensitive dye transfer sheets may comprise a photoconductive zincoxide coating on one surface and separate coatings of magenta, yellowand cyan dyes in sequence on the reverse surface. With these three dyesa close approximation of the colored original may be formed.

The dye source sheet 15 may contain a single dye or a mixture of dyes,and in any desired concentration, depending on the specific color andintensity desired for the background areas. Ethyl cellulose is apreferred binder and toluene a preferred solvent, although othermaterials may be used. The addition of an inert powder such as silicapowder is helpful both in obtaining a smooth homogeneous coatingComposition and in obtaining rapid and uniform transfer of dye.

The dyes employed in the dye source sheet should have sub stantially thesame volatility as those of the photosensitive dye transfer sheets, andindeed the identical dyes may be used in both instances. Specificexamples include N,N-dielh vl-ptricyanovinyl aniline as the magenta dye.Sudan Yellow G.R. Conc. as the yellow dye, and2-chloro-2'-methyl-n,n-diethylindoaniline as the cyan dye. A typicalcoating formula includes 7.9 parts by weight of ethyl cellulose, 1 partofpowdered silica (Syloid 244), 91.1 parts of toluene, and 1 part ofmagenta or cyan dye or 1.5 parts of yellow dye. Smooth coatingproperties are obtained by thorough homogenization of the mixture and byselection of an ethyl cellulose of appropriate viscosity or by variationin the proportion of volatile solvent. The several mixtures are coatedon 37 lb. paper at a coating weight, after drying, ofapproximately 9.4g./sq. ft. (4.3 g./sq. m.). Mixtures of these same dyes may be used toprovide other desired colors. As an example, a coating containing 0.9part of the cyan dye and 0.1 part of the magenta dye produces a deepblue color on the receptor sheet. Again, a coating containing 0.24 partof the magenta dye and 0.013 part of the yellow dye produces a pastelpink color on the receptor sheet.

An illustrative procedure will now be described. A first photosensitivedye transfer sheet is placed against a porous paper temporary receptorsheet on a vacuum platen and a vacuum is established, holding the two inclose contact and in fixed position. The transfer sheet carries a dyecoating on the surface contacting the receptor sheet, and aphotoconductive zinc oxide coating on the outer surface. The outersurface is exposed to a color separation light image from a positivecolor print original, to impart a latent image. A conductive rollercarrying a coating of conductive radiation-absorptive toner particlesand at a high potential is passed over the exposed surface to deposittoner at the nonlight-struck areas. The surface is then briefly exposedto intense infra-red radiation, causing transfer of dye to the temporaryreceptor at the infrared absorptive toned areas. The vacuum is released,the photosensitive sheet is removed and replaced with a secondphotosensitive sheet carrying a second dye, and the process is repeatedusing an appropriate color separation filter. The process is againrepeated using a third filter and sensitive sheet, to produce a fullthree-color intermediate but of dull, lifeless appearance.

One or more portions of the intermediate, for example three detailsections as indicated by segments 12-14 of FIG. 1, are cut from thesheet. These segments are placed against a transparent dye-receptivefilm in desired arrangement, and over them is placed a paper dye sourcesheet having a blue dye coating as previously described herein but minusthe photoconductive coating of the transfer sheet. The three layers arepressed together and briefly heated, i.e., for 2 minutes at 275 R,either between platens as in FIG. 1 or by holding under tension over asingle convexly curved platen. The film is removed and is found toretain a brilliantly clear full color copy of the detail sections on anequally clear blue background.

The dye-receptive film consists of a transparent Mylar polyester filmcoated with a transparent coating of a mixture of 1.5 parts of nickelacetate tetrahydrate and 10 parts of polyvinyl alcohol, applied fromsolution in Water which may if necessary contain just sufficient wettingagent and antifoaming agent to provide smooth uniform coatingcharacteristics.

The dry weight of the coating is about one-half g./sq. ft. (5.4 g./sq.m.). The coating serves as a solvent and fixative for the dyes so thatthe colored areas do not cause diffusion of light transmittedtherethrough and the colored film serves as a color projectiontransparency. Similar coatings may be applied to nontransparentsubstrates, e.g., to paper or metal, where transparency is not required.

What is claimed is as follows:

1. Method of simultaneously imprinting a colored design and a coloredbackground on a permanent color receptor sheet comprising applying asaid design in volatilizable dye to a temporary intermediate receptorsheet segment, placing said segment against said permanent receptorsheet, placing a color source sheet carrying a volatilizable dye oversaid segment and against said permanent receptor sheet, and heating saidsource sheet to an extent sufficient to cause transfer of said dyes tosaid permanent receptor sheet, the said segment serving as a mask forpreventing the dye from reaching said permanent receptor sheet from saidsource sheet at the masked area.

24 Method of claim 1 wherein said intermediate sheet is a porous paperand said design is applied to said paper by selective transfer of dyefrom separate monocolor source sheets by selective heating of colorseparation image areas while said source sheets are in closepressurecontact with said intermediate sheet.

3. Method of claim 1 wherein said permanent receptor sheet is a cleartransparent film having at least a surface stratum in which said dye issoluble.

4. Method of claim 2 wherein the porosity of said intermediate sheet issufficient to permit attaining close contact between said sheet and aphotoconductive zinc oxide coated dye transfer sheet on a vacuum platen.

5. Method of claim 3 wherein said surface stratum comprises a nickelsalt and polyvinyl alcohol.

6. Method of claim 1 wherein said color source sheet is uniformly coatedover one entire surface with said volatilizable dye.

2. Method of claim 1 wherein said intermediate sheet is a porous paperand said design is applied to said paper by selective transfer of dyefrom separate monocolor source sheets by selective heating of colorseparation image areas while said source sheets are in closepressure-contact with said intermediate sheet.
 3. Method of claim 1wherein said permanent receptor sheet is a clear transparent film havingat least a surface stratum in which said dye is soluble.
 4. Method ofclaim 2 wherein the porosity of said intermediate sheet is sufficient topermit attaining close contact between said sheet and a photoconductivezinc oxide coated dye transfer sheet on a vacuum platen.
 5. Method ofclaim 3 wherein said surface stratum comprises a nickel salt andpolyvinyl alcohol.
 6. Method of claim 1 wherein said color source sheetis uniformly coated over one entire surface with said volatilizable dye.